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A ground-based follow-up study of potential targets of the asteroseismic satellite mission COROT

Final Activity Report Summary - PREPCOROT (A ground-based follow-up study of potential targets of the asteroseismic satellite mission COROT)

Stars are the fundamental building blocks of the universe, but unfortunately their interior is not directly observable. The only available quasi-direct way to obtain information on their internal is by means of stellar pulsations, which can be observed and identified through line-profile and light intensity variations. Pulsation frequencies and mode parameters carry information on the routes that the waves have travelled, that can be exploited to probe the stellar interior. This field of astrophysics is called asteroseismology. A new era in asteroseismology is opening with the CoRoT satellite mission, which focusses on asteroseismic studies and the search for exo-solar planets. The main objectives of this project were to contribute to the ground-based monitoring, analysis and characterisation of potential primary and secondary targets of the CoRoT satellite, and in particular of the delta Sct and gamma Dor type, to be ready to interpret the rich pulsational frequency spectrum, which will be derived from the space monitoring. The project was oriented in a large team of international scientists.

An important factor for meeting the aims of the Fellowship was the successful launch and subsequent operation of the CoRoT satellite from December 2006 onwards, and the acceptance of several Large Programme and normal observing proposals, guaranteeing observing time with the best spectroscopic and photometric instruments. Therefore, our first objective, to build up a photometric and spectroscopic time-series for a selection of CoRoT primary and secondary targets, has been successfully carried out during the fellowship. The data has also been made available to the asteroseismic CoRoT comunity.

In the framework of the Fellowship three pulsating stars belonging to different pulsational classes along the Main-Sequence were subjected to a detailed pulsational analysis. Hereby, the Marie Curie Fellow expanded her expertise in pulsational studies from massive early-B type stars to lower-mass pulsators. By analysing both photometric and spectroscopic time-series she obtained skills in the treatment and analysis of multi-colour photometry, to complement her expertise in spectroscopic data analysis.

From a photometric dataset the Be nature of V2104Cyg was discovered, and three pulsational frequencies were detected. The fast rotation of the star hampered the identification of the modes and enabled the Fellow to explore the limits of the underlying theoretical models.

Analysis of a large data set of ground-based observations of the beta Cep CoRoT target HD180642 confirmed the presence of a dominant radial mode, and revealed evidence for a few additional non-radial pulsations modes, including a possible high-order g-mode. The presence of both high-order g-modes as low-order p- and g-mode makes this target extremely suitable for a profound asteroseismic study.

One of the main achievements of the analysis of the gamma Dor CoRoT target HD49434 was the detection of its hybrid nature. At least four gamma Dor-type frequencies as well as five frequencies in the expected domain of delta Sct pulsations are present. Hybrid stars are particularly interesting from an asteroseismic point of view as they provide simultaneously information on both the deep interior (g-modes) and the envelope (p-modes) of the star. All modes, for which an identification was possible, were identified as high-degree modes, which will make future modeling challenging. The ground-based multi-site multi-instrumental dataset of HD49434 compiled and analysed during the Fellowship is the most extensive available for a gamma Dor variable to date.

The results obtained satisfy the second objective 'to characterise the pulsational behaviour of several Main-Sequence pulsators, to be ready to interpret the rich pulsational frequency spectrum which will be derived from the space monitoring'. Exploitation of the CoRoT satellite data will be needed to unveil ambiguities in the detected pulsational frequencies and to increase the number of well-identified pulsation modes.